Storage library systems are often used by enterprises and the like to efficiently store and retrieve data from storage media. In the case of some storage libraries, the media are data cartridges (e.g., tape cartridges) that are typically stored and indexed within a set of magazines. When particular data is requested, a specialized robotic mechanism finds the appropriate cartridge, removes the cartridge from its magazine, and carries the cartridge to a drive that is designed to receive the cartridge and read its contents. Some storage libraries have multiple drives that can operate concurrently to perform input/output (IO) operations on multiple cartridges.
To operate properly, the robotic mechanisms are expected to reliably (e.g., repeatably and accurately) and rapidly find, retrieve, and deliver desired cartridges throughout the storage library cartridge inventory. This functionality can be facilitated by configuring the robotic mechanism to move a hand assembly in at least three axes (e.g., x, y, and z directions, and sometimes one or more of pitch, roll, or yaw), and to include one or more sensors to reliably detect the position and/or orientation of the hand assembly. When in its desired location, the hand assembly is activated to reliably grip the desired cartridge and remove it from a magazine or drive, or to reliably release the cartridge into a desired magazine slot or drive.
Each degree of freedom provided to the robotic mechanism becomes a potential source of accumulated error when positioning grip components of the hand assembly. For example, even if the hand assembly is parked in such a way that it can only move rotationally using its “wrist” mechanism (e.g., in a yaw direction), errors accumulated from one or more components can adversely impact wrist positioning precision, thereby affecting reliable location and/or pointing of the grip components. Some traditional implementations attempt to address these accumulated tolerances through one or more feedback mechanisms, including sensors, stepper motors, alignment features, or the like. However, these traditional types of techniques can add cost and/or complexity to the implementation and, in some cases, additional sources of potential error.
Accordingly, it may be desirable to provide a reliable mechanism for accurate positioning of the wrist mechanism at a desired wrist angle without complex and/or costly feedback techniques.